This invention relates to an electronically controlled fuel injection system for injecting fuel into the intake system of an internal combustion engine.
A conventional electronically controlled fuel injection system has a basic construction as shown in FIG. 1. As shown in the figure, a throttle valve 4 is arranged in an intake pipe 3, the interior of which communicates with a combustion chamber 2 of an internal combustion engine 1, and a fuel injector 5 is provided downstream of the throttle valve 5. The fuel injector 5 is connected to a fuel pump 7 via a fuel supply pipe 8 to pressure deliver fuel from a fuel tank 6 to the fuel injector 5. A pressure regulator 9 is arranged across the fuel supply pipe 8 to regulate the pressure of fuel. Further, the system also includes an intake pressure sensor 10 for detecting intake pressure (P.sub.B) in the intake pipe 3 at a location downstream of the throttle valve 4 and an engine rotational speed sensor 11 for detecting the rotational speed (Ne) of the engine 1. Signals from these sensors are supplied to an electronic control unit (hereinafter referred to as "the ECU") 12. The ECU 12 controls the amount of fuel injected by the fuel injector 5 based on the detected values of the intake pressure (P.sub.B) and the engine rotational speed (Ne).
In the conventional fuel injection system, the fuel pump 7 is required to achieve high delivery pressure in order to secure a predetermined injection pressure (e.g. 2.5 kg/cm.sup.2), which results in an large size of the fuel pump 7 as well as a high manufacturing cost.
In the meanwhile, it has been proposed, by Japanese Provisional Patent Publication (Kokai) No. 63-170557 and Japanese Provisional Patent Publication (Kokai) No. 56-9653, for example, to arrange the nozzle of the fuel injector such that it faces a venturi formed in an intake passage of the engine, to thereby make the fuel pump 7 smaller in size or dispense therewith. However, the proposed fuel injection systems have the inconvenience that it is very difficult to control the amount of fuel injection.